final switch usage

[#ponce]

For the low-level programmer, sometimes you must use switch because virtual functions are more expensive (cache usage...) and pointers to functions too.

The problem is that even if the optimizer turn the switch into a jump-table, it has generally no clue about whether the value will be in the right range. Only static analysis could do that and in C/C++ well...

So in C++ production code I'm currently forced to use something like this :


---------------------------------------------
#pragma_assert(x >= 0)
#pragma_assert(x <= MAX)

switch(x)
{
  case 0: doSomething0(); break;
  case 1: doSomething1(); break;

...

  case MAX: doSomethingMAX(); break;
}
---------------------------------------------

to make the optimizer know that i'm in the good range and drop the runtime check (such conditionnals breaks pipeline).

My proposition is that final switch does a runtime check and eventually throw an exception in debug mode, but does not check anything in release mode. It would be consistent with how ArrayBoundsException works. 

It may seems a stupid request since I don't know how final switch works currently. 

But my feeling is that it would make the fastest possible dynamic dispatch, without loosing reliability. This could be very valuable for people interested in performance.